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Exploiting Weight Data to Support Engineering and Corporate Decision-Making Processes (Paper)

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Weight control, from early weight estimation through life cycle weight tracking, is often conducted in dangerously inefficient ways or, worse, not conducted at all. Despite a general agreement on the utter importance of weight and centre of gravity calculations, during all phases of ship design, construction and operation, only seldom does weight data receive the attention and appreciation it requires on a corporate-wide scale. This paper will explore the nature of weight data, the tools available for weight control at the various stages through the life cycle of a water-bound vessel, and identity various players who influence the weight of a vessel.
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    334   Exploiting Weight Data to Support Engineering and Corporate Decision-Making Processes Nick Danese , Nick Danese Applied Research, Antibes/France, ndar@ndar.com  Runar Aasen , BAS Engineering, Aalesund/Norway, runar@shipweight.com Abstract   Weight control, from early weight estimation through life cycle weight tracking, is often conducted in dangerously inefficient ways or, worse, not conducted at all. Despite a general agreement on the utter importance of weight and centre of gravity calculations, during all phases of ship design, construction and operation, only seldom does weight data receive the attention and appreciation it requires on a corporate-wide scale. This paper will explore the nature of weight data, the tools available for weight control at the various stages through the life cycle of a water-bound vessel, and identity various play-ers who influence the weight of a vessel. Examples of weight data sharing techniques and scope will also be reviewed. Finally, the means of implementing an effective weight policy will be described, and the benefits evoked. 1. Introduction Weight control, from early weight estimation through in-service weight tracking, is often conducted in dangerously inefficient ways or, worse, not conducted at all. Despite a general agreement on the utter importance of weight and centre of gravity calculations, during all phases of ship design and construc-tion, weight data never seems to receive the attention and appreciation it requires. There are many reasons behind this somewhat conscious disregard, spanning from the cultural to the technical. Cultural reasons include lack of or limited knowledge of the weight subject itself, lack of statutory requirements (with the notable exception of some Navies), overconfidence in weight related consid-erations, incorrect appreciation of ships' similarities (or lack thereof), etc. Technical reasons include a limited market offer of dedicated, appropriate engineering tools, limited facilities for interfacing with CAD, limitations in many CAD tools, absence of managed feed-back from production management, difficulties in combining weight data into corporate management processes, etc. The contradiction between the paramount importance of Weight and CG for a ship and the all too common disregard for these quantities is striking, as if the consequences of underplaying the impor-tance of weight data were not damaging at best, catastrophic at worst. While at least some of the cul-tural reasons behind a correct and responsible approach to weight and CG calculations can be wiped by the use of appropriate technical tools, the fact remains that today only few technical tools lend themselves to an effective and reliable implementation of a constructive weight policy, able to support both the engineering and corporate decision making processes. In this paper, for simplicity, we will refer to both weight and centre of gravity as weight, and we will review how the targeted use of state-of-the art IT technology can already today offset virtually all technical obstacles to the encompassing implementation of a corporate-supporting weight policy, as well as the cultural ones. 2. Weight, the skeleton in the closet Weight is arguably the most common factor behind unachieved design and contractual goals, and generally the most difficult one to work with when it comes to identifying the genesis of error. The weight quantity exists in various forms during the life time of a ship: -   Macroscopic estimation at the very early stages based on a general mission statement and ship type selection.    335   -   Estimation coupled with the development of feasibility study and conceptual design. -   Estimation evolved in parallel with pre- and contract reviews. -   Integration of CAD data during design. -   Integration of as-built data during production. -   Integration of in-service weight data to improve realism and quality of historical data 3. Weight groups and weight items It is important to distinguish between weight groups and weight items, a distinction which is often overlooked, and to their complementarities. Weight groups represent a range of unspecified but certainly present weight items. Weight items are be collected within weight groups, at the various levels in the weight model hierarchy. The weight value of a weight group can be estimated using macroscopic ship parameters such as type, mission profile, etc. For example, within a specific ship type, the weight of the engine room can be accurately estimated from ship size, service profile, etc. On the contrary, despite mostly containing the same equipment and machinery by nature, the engine room of a tanker will be identifiably different from the engine room of a tug or of an Offshore Supply Vessel and therefore one can hardly estimate the weight of the tanker's engine room from the know weight of an OSV's engine room. More immediately identifiable to the layman, weight items are just that, individual components of the ship. While there are tools and ways to add up almost all the components of a ship, a complete list of all the items making a ship is simply not available until the ship's construction is truly completed, therefore an item list becomes a reliable approach to weight control only at later stages of the vessel's genesis. The importance and usefulness of weight groups is therefore evident, from the very first stages of the ship design process. It also follows that weight groups and weight items are complementary, and that both are required to carry out a constructive weight control strategy. Furthermore, it is important to factor in the too often disregarded yet very real role of non-engineers in the weight determination process. For example, consider the specification of heavy equipment, often dictated by price rather than absolute technical specifications or performance measurement, or by availability, and which may not be defined until a later stage in the design process. Then, perhaps surprisingly to some, it becomes clear that weight is influenced by many different play-ers within the corporate panorama, and that communication between them can only be beneficial to the success of a corporate weight strategy. 4. Weight data organization In the more rational approaches, weight groups and weight items are organized in hierarchical data structures generally referred to as Weight Breakdown Systems (WBSs). Various WBSs have been developed ever since ship design became a formalized discipline, but they can be exploited most effi-ciently only since the invention of relational databases. On the other hand, the eternal, ubiquitous spread-sheets do not lend themselves well to the use of WBSs, because the macroscopic aspects of discriminating weight calculations made possible by the use of WBSs are very difficult to implement therein. In WBSs, weight groups are organized in hierarchical fashion: for example, let us refer to the NATO WBS, used by many Navies and, until recently, more generally across the ships industry.    336   Easy to guess, weight items are collected within weight groups. But, perhaps less easy to guess, not all weight groups are made to collect weight items. The reason for this is that higher level weight groups lend themselves well to predictive regression analysis, and at this rather macroscopic level individual weight items are not relevant. Of course, advanced software tools do allow the adding of the odd weight item even at the higher levels of a WBS. Over time, several industry-standard WBSs have been developed from the one or two primitive WBSs of old, and they are loosely referred to in most weight estimation and weight tracking work. However, while it is always tempting to develop one's special WBS in the quest of perfecting the weight pre-diction exercise into a most accurate result, one must be careful to maintain sufficient homogeneity in the general WBS structures being used to allow the identification of similarities not only between ships of the same general type, but also, very importantly, between ships of different types. In fact, ignored by many, it is this very ability to identify similarities within and across ship types that constitutes the basis of the most powerful and accurate weight estimations, and which can contribute the most to the overall corporate ship design and ship building process from the earlier stages. To keep to the corporate environment addressed by this paper, let us just remind ourselves of the relation-ship between weight and quantity (ex. steel plates) and between weight, production planning and fi-nancial planning (when will how much steel be required to support the planned production schedule?). 5. Weight Calculation Tools Various tools of disparate nature are used for weight calculations. Concisely, tools lending themselves to weight data management can be grouped in major categories: -   Design tools -   Production tools -   Corporate tools Across the categories listed above, the tools most used in weight data management range from the application of simple macro-multipliers, to the ubiquitous but intrinsically limited MS-Excel, to dedi- A brief history of Ship WBS ã   since the 30th century BC: imaginative intuition, gut feeling, luck ã   since the 19 th  century : weighted, proportional extrapolation, simple statistical analysis ã   sometime in the 20 th  century - Ship Work Breakdown Structure (SWBS) ã   1970s onwards - pre-spreadsheet, in-house development of computerized weight tracking ã   mid-1980s - advent of the spreadsheet ã   1988 - Expanded Ship Work Breakdown Structure (ESWBS) - the functional configura-tion definition of the ship is improved and expanded to serve logistics support, to become a integrating, common reference point from design through operation, allowing life cycle data to become an intrinsic contributor to the ship design process ã   early 1990s - Commercial Ship WBS developed by BAS Engineering, Norway - departure from the US Navy-srcinated and NATO adopted SWBS, and from the ESWBS, to ac-commodate the different product model nature of and predictive algorithms required by commercial ships of different types.   Fig.1: Brief history of the ship WBS      337   cated software applications custom developed by individual companies for in-house use and, finally, to encompassing commercial products like ShipWeight, by BAS Engineering, Norway. Unfortunately, to date, general CAD and corporate software tools are not commonly considered to be a default integral part of a coordinated, corporate-wide weight policy. To make matters worse, many such tools lack even the simplest connectivity features, making data exchange virtually impossible. Fig. 2: Later version of the US Navy SWBS was used as the base of most modern SWBSs   5.1 Design tools Referring to Section 2, design tools will be used until and throughout the integration of CAD data during design work. Design tools can be further grouped by the design phase during which they are used. For example, we could identify: -   Conceptual design tools -   Preliminary design tools -   Contractual design tools -   Detailed Design tools There are of course tools which span the realm of the above, and they will be addressed separately. The aim at the conceptual stage of design is to identify the overall weight of the ship, and to validate the estimated weight by analysing second and perhaps third level weight groups for congruency and consistency as a function of the mathematical methods employed. Conceptual design tools span the range from simplistic macro-multipliers to top-WBS level prediction methods. For example, if a rela-tional database is available, one can regress a weighted and qualified interpolation through a historical database data set, using appropriate coefficients and drawing from a heterogeneous library. Preliminary design tools are used to validate and converge the conceptual weight estimation. If a hier-
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